Make your ClientID class static and make all the methods static. Then you can do ClientID.getID from any of your classes and it should contain the variable.

You wouldn't have to instantiate the ClientID class in your main method then.

I would strongly advise against using static anything here as it is very anti-OOPs and completely unnecessary. What is a stand-alone static class anyway?

Instead the classes that display your info and that add new or change it should have public methods that the main class can use to extract info as needed. Also, you shouldn't be displaying new JFrames here, but rather dialogs such as JDialogs.

OK, a bloated example that uses a JList instead of a JTable and a HashMap instead of a database for simplicity (and cuts other corners too), but it does illustrate the point. Sorry for the lack of comments, but it was composed quickly...